Jet engine silencer nozzle structures with tapered apertures in outer walls



I Unlted States Patent [1113,543,876

[72] lnventor John E. Karlson 2,528,674 ll/1950 Thomaswm... H 181/41XNassau County, New York (423 Bedell 2,601,655 6/1952 Young 239/601XTerrace, West Hempstead, NY 11552) 2,788,184 4/1957 Michael 244/53.8[21] Appl. No. 703,080 2,816,619 12/1957 Karlson 1111 181/27 [22] FiledFeb. 5,1968 2,856,022 10/1958 Kurtze et al. 181/.5 Continuation ofSer.No. 486,392,8ept. 10, 2,959,916 1 H1960 Carlton et a1. 181/3321 1965,abandoned. 2,968,150 1/1961 Goebel et a1... 239/601X [45] Patented Dec.1,1970 3,163,379 12/1964 McLafferty .v 244/53.8 3,314,611 4/1967McCartney et a1. 239/601X 2,553,443 5/1951 Davis. 181/3322] 2,986,0025/1961 Ferai 181/33.221 s41 JET ENGINE SILENCER NOZZLE STRUCTURES i gWITH TAPERED APERTURES 1N OUTER WALLS 3 1 H1965 A d 18l/33221 14 Claims22 Drawing Figs. r oin Primary Examiner-Robert S. Ward, Jr. [52] US. Cl1188151732, mmmey Kenyon Kenyon Remy Ca" & Chapin [51] lnt.Cl F0ln l/14,

7/20 ABSTRACT: This invention relates to a design for condition- [50]Field ofSearch ..239/265.11, ing the flow offluid passing through atubular structure, and to 589; 137/1 H5/l6' 14; a method of controllingthe pressure and velocity offluids and 181/3322 431 721 theaccelerations thereof. Specifically, the design is a tapered 244/53-8aperture in the wall ofthe tubular structure through which the l flow offluid is assing. The a erture or slot is substantially [56] ReferencesC'ted longitudinal and ias its greatest transverse width dimension atUNITED STATES PATENTS the general opening of the tubular structure. Fromthe region 538,861 239/601X of maximum width it continuously convergesto a point of 829,033 8/1906 Ronstrom......!..........

5/1895 Boehmen minimum width and closure.

Patented Dec. 1, 1970 Sheet 1 or 3 FIGS FIG.4

FIGB

l N VENTOR. JOHN E. KARLSON Patented Dec. 1, 1970 Sheet L o! 3 FIG. I I8FIGIB FIG. IO

FIGIS I N VIZN JR JOHN E KARI-SON A77 R/VEXS Patented Dec. 1, 1970 Sheet3 I6; I8 I FIG. I9

I N VliN'l'OR. JOHN E. KARLSON BY 3 ATTORNEYS FIGZI JET ENGINE SILENCERNOZZLE STRUCTURES WITH TAPERED APERTURES IN OUTER WALLS CROSS REFERENCETO RELATED APPLICATIONS This invention is a continuation of applicationSer. No. 486,392 filed Sept. 10, 1965 by John E. Karlson and nowabandoned. Other continuation applications of said application Ser. No.486,392 are being filed simultaneously herewith and are entitledMicrowave Energy Conditioning Device" and Improvement in AcousticTransducers.

FIELD OF INVENTION This invention is directed to the provision ofexhaust nozzle ducts for jet or rocket propulsion power plants, and alsoto the provision of air inlets for jet power plants. It has been foundto have application to the field of fluid flow generally, and in anyenvironment wherein fluid flow is entering or leaving a tubularstructure.

DESCRIPTION OF THE PRIOR ART The prior art includes jet engine exhaustnozzles and air inlets which are provided with perforations or slots inthe walls. None of these designs'suggest the use of tapered apertures,particularly not those which have their maximum width at the inlet orexit opening, nor the use of such nozzles, inlets or fluid handlingmethods as disclosed herein.

The present state of the art lacks and utterly fails to recognize theuse and usefulness' of a fluid flow structure which is formed with atapered aperture at either the inlet or exit, a design that is uniquelysuited to achieving an increase of air intake or thrust, and also toreducing the noise that attends the passage of fluid flow in suchsituations. This lack is particularly noteworthy since considerable timeand money has been expended in jet engine development to effect designsthat will increase thrust and reduce noise.

A tapered aperture in a coupling chamber for loudspeakers and otheracoustical systems, is disclosed in US. Pat. No. 2,816,619, issued onDec. l7, 1957 to John E. KarlsomTriangular apertures have also beenapplied on loudspeaker systems. See, for example, German Pat.application No. 1,137,483 issued on Oct. 4, 1962 to Lothan Cremer.

That patent is directed to providing a design for coupling chambershaving acoustical application which incorporate the critical geometry ofthe subject tapered aperture. The utility of providing a taperedaperture in a pipethrough which sound waves are passing is explained isthe theory of the phenomenon occurring as sound waves pass through thetapered opening.

An acoustic coupling chamber differs markedly from any structure throughwhich a flow of fluid might pass. The acoustic art is not analogous tothe fluid flow art. Consequently, the Karlson US. Pat. No. (2,816,619cannot be read to teach or suggest placing a tapered aperture in eitherthe inlet or exhaust of a structure through which fluid flow passes.Moreover, it cannot be said to be obvious to one skilled in the art offluid mechanics to'construct a fluid conveying tubular structure withatapered aperture at either terminus from the disclosure of the KarlsonUS Pat. No. (2,816,619).

BACKGROUND OF INVENTION The first requirement in reducing the noise fromsuch engines is that of minimizing the factors which will tend toproduce noise in the presence of rushing gases. These rushing gasesoccur both in the intake and exhaust. The factors which will add to anyinherent noise present are turbulences, resonances. and mechanicalvibrations. If these can be minimized, naturally the overall noise levelwill be reduced. Turbulences are caused by sudden changes in pressure ina gaseous flow. Methods of handling flow with gradual accelerationsavoid such changes, and turbulences because they avoid creating suchsudden changes of pressure. In this instance, the gaseous flow is insidea tubular structure.

While such a flow is along a continuous length, and the rate of flow andpressure is relatively constant, there is apparently a minimum degree ofturbulence created in this air flow. How ever, as soon as the rapidlyflowing gases reachthe end of the tube, abrupt changes occur in thepressure contours within the tube and severe turbulences are generated.

Studies have shown that the noise generated by such turbulencesincreases as the eighth power of the rate of flow. Control of suchturbulences therefore presents the greatest opportunity for improvementin reducing jet noise.

A reflective flow is created at the end of the tube due to abrupttransition at the end of the tube, which reflective flow travels downthe tube in opposition to the main flow. This creates additionalturbulences and a reduction in the rate of flow.

To compound the situation reflected waves create the conditions forresonance and still more noise. The noise generated by such turbulencesand the resonances represent lost energy and a subsequent loss inefficiency in the engine, in addition to the annoyances created by the.high level noise in the vicinity of such engines. Lost efficiencies mustbe made up by still higher velocities and still more noise.

FIG. 2 shows how a tapered aperture can be included in both air intakeand jet exhaust of a jet engine. During operation the high pressuresdeveloped by the combustion of the fuel will create a flow toward theregion of minimum pressure. The greater the pressure differential, thehigher will be this rate of flow, and the greater the efficiency of thejet engine.

If a curved focusing wall and a low-pressure starting (starter) regioncan be established near the center of combustion, the directivity ofsuch flow can be established with a minimum of turbulence. Also, if thejet chamber region presents over lower pressures in a smooth continuousfashion, the flow thus started will accelerate to the maximum degree.This smooth continuous change in pressure will simultaneously eliminateor strongly reduce theprincipal cause for turbulence, namely, abruptchanges in pressure. Similarly, since no abrupt change in pressureoccurs, the conditions for acoustic resonance in the exhaust tube arealso removed. As a result, under these conditions, the noise attendantto such combustion and exhaust will be reduced to a minimum. Inaddition, the increased rate of flow will improve the efficiency of of atube through which fluid flow energy is passing will effec- 1 tivelyreduce the deleterious noise associated with the passage of fluid energythrough the tube. ln addition, the inventor has discovered thatproviding a tapered aperture in either the air inlet or exhaust nozzleof a jet or rocket propulsion engine through which fluid energy isadapted to pass will improve the engine efficiency, intake of air andthrust and that higher velocities of exhaust can be obtained and higherpressure applied to the nozzle without choke.

It is an object of the present invention to provide a method of handlingfluid. flow and a design for a tubular structure to practice'themethodthrou'gh which a flow of fluid will pass at high velocities with amaximum intake or thrust, and minimum turbulences, resonance, and noise.

It is a further object ofthe invention to provide a critical geometricalconfiguration for air inlets and exhaust nozzles which will increase theefficiency of the engines in addition to reducing the attendant noise.

These objects and others, as'will be apparent from the disclosure anddiscussion hereof, can be achieved by providing this structure throughwhich a flow of fluid'is passing. Basically, the tapered aperture willbe identically configured regardless of whether it is in the inlet orthe exit of the tubular structure. Specifically, the aperture isconfigured to have its largest width dimension at the inlet or exitopening and taper inwardly, rearwardly or forwardly respectively, to apoint at which it terminates. The length of the tapered aperture is un-.derstood to be more than one-half the effective length of the tubularstructure associated with the inlet or exhaust nozzle and the width ofthe aperture at the opening, wherein the width is greatest, must begreater than one-half the width of the inlet or nozzle opening.

DESCRIPTION OF DRAWINGS The invention will be described further by wayof example with reference to accompanying drawings wherein:

FIG. I is a side view of a tubular structure through which a flow offluid passes whichhas the subject invention incorporated therein;

FIG. 2 is a perspective view of a jet propulsion engine showing thetapered aperture of the subject invention in both the air inlet andexhaust nozzle, with wing segment. It is to be understood that theorientation of the tapered apertures has.

been selected for convenience of illustration;

FIG. 3 is across-sectional view taken through lines 3-3 of FIG. 2; I

FIG. 4 is a cross-sectional view taken through lines 4-4 of FIG. 2;

FIG. 5 is a cross-sectional view taken through lines 5-5 of FIG. 2; v

FIG. 6 is a cross-sectional view taken through lines 6-6 of FIG. 2;

FIG. 7 is a cross-sectional view taken through lines 7-7 of FIG. 2;

FIG. 8 is a cross-sectional view taken through lines 8-8 of FIG. 2;

FIG. 9 is a perspective view of the exhaust section of a jet of rocketengine provided with tapered apertures of the subject invention;

FIG. 10 is a perspective view of a fire hose configured to include thetapered aperture of the invention;

FIGS. 11A and l lB are perspective views of fluid injectornozzlesconfigured to include tapered apertures of the subject invention.

- FIG. 12 is a perspective viewof a hydrojet configured to include thetapered aperture of the subject invention.

FIG. 13 is a side view of amuffler with the noiseless exhaust outletconfigured to include'the tapered aperture of the subject invention.

FIG. 14 is a side view of the subject invention shown provided withinwardly rolled edges.

FIG. 15 is a sectional view of FIG. 14 through lines 15-15.

FIG. 16 is a side view of a rocket having an exhaust nozzle according tothe present invention.

FIG. 17 is inlet or nozzle having a sound shield turbulence suppressorthereon.

FIG. 18 is a side schematic drawing of the front portion of a jet enginehaving an inlet according to the present invention.

FIG. 19 is a side schematic drawing of a rocket having an exhaust nozzleof the present invention.

FIG, 20 is a drawing showing the aspiration achieved by a nozzle of thepresent invention.

FIG. 21 is a drawing showing the predominate flow, believed to belaminar in nature, from anozzle of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT A general design of the subjectinvention is shown in FIG. I which depicts a tubular structure 2 throughwhich a flow of fluid is to pass. The tubular structure 2 is constructedto provide an inlet chamber 4 and an exit chamber 6 which have taperedapertures 3 and 5 respectively formed therein.

The tapered aperture 3 of the inlet chamber 4 converges from inletopening 9, its point of maximum width, to point 7, wherein itterminates.

Conversely, the tapered aperture 5 of the exit chamber 6 convergesforwardly from exit opening 10 to point 8 wherein it terminates.

It is important that the length of the tapered aperture 3 and 5 begreater than one-half the effective length of the respective chambers 4and 6 if the chamber is to be substantially detuned or nonresonant. Theapproximate effective length of inlet chamber 4 is indicated bydimension a while the effective length of exit chamber 6 is shown bydimension a.

The length of a chamber as described in this invention may be defined asthe distance from the position where the widest portion of the taperedaperture occurs (near the end) to the position where the prevailingcontinuity of said chamber ends. That continuity ends at a substantialsudden change in unobstructed cross-sectional area of the chamber, achange usually of about at least 50 percent of the total such area. Forexample, in turbojet engines the length of this chamber would includethat section which is normally regarded as the nozzle structure, whileit would not include the complex structure and turbines involved in theturbojet engine itself. Location 52 illustrates one end of such achamber, while Location 45 illustrates the other end of the same chamberand the distance between these positions constitutes the length.Similarly, at the air intake the length involved would not include anyvolume internal to the turbofan. Where a multiplicity of tubes is usedas in FIG. 9, the length of the chamber would be that of each individualtube as qualified by the above definition.

Another important dimension for the configuration of the apertures 3 and5 is the maximum width. As seen in FIG. I, the maximum width of thetapered apertures 3 and 5 is located at the respective openings 9 and 10of chambers 4 and 6 and'is desirably the full width of the chamber asshown. The maximum width of the tapered apertures 3 and 5 should be atleast greater than one-half the diameter of the tubular structure at thepoint of such maximum width.

Another important criterion for the configuration of the v apertures isthat they be tapered. The desirable taper configurations which have beenused are shown in the attached drawings, which have been drawn to scaleas closely as possible for the different configurations which are shown.It will be appreciated that there can be deviations from the optimalcurvatures, the best now known being shown, but that substantialdeviation will be accomplished by a deterioration in performance. Thiscurvature can be readily applied to various nozzles in different designapplications by those skilled in the art by the teaching therein.

As previously indicated the tapered aperture has application in anystructure through which a flow of fluid is passing. However, it has beenfound in practice to produce particularly good results when used in avacuum cleaner analog for the air inlet and exhaust nozzle section of ajet propulsion engine. This vacuum cleaner analog is constructed of anordinary tank-type vacuum cleaner, with the bag and any air filters ordust filters removed, and with'the nozzles adapted to be attacheddirectly at either or both ends, without use of intervening hose orextension pieces. The vacuum cleaner may be mounted on frictionlessbearings and, for example, large lightweight rollers, and a spring scaleheld against the front of the cleaner to record thrust.

The tapered aperture of this invention is shown in FIG. 2 embodied in ajet propulsion engine 12 mounted on an aircraft wing 18.

The tapered aperture of this invention is depicted in air inlet section14, seen in FIG. 2, as slot 43 which extends from the air inlet opening53 to a point 55. For optimum inlet performance, the length of the slotor aperture 43 should be greater than one-half the effective length b ofair inlet section 14. In addition, slot 43 must have its greatest widthdimension at the inlet opening 53. The dash line 57 seen in FIG. 3indicates the size of the tapered aperture air inlet at line 3-3 of FIG.2. The width of the opening of the slot 43 while not limited to anyexact size, should be greater than the width w of the tube to affordoptimum performance. FIGS. 4 and 5 which are sectional views takenthrough the air inlet section 14 show the taper of aperture 43 alonglines 4-4 and 5-5 to point 55 where it terminates.

The provision of a curved surface-as shown at 56 opposite aperture 43will improve the directivity of the flow therethrough. However, it isnot imperative that the air inlet or exhaust nozzle provided with thetapered aperture of the subject invention have a curved inner surfaceopposite the tapered aperture.

The nozzle section 14A of the jet engine is provided with:a taperedaperture 45A similar to the aperture 43 in the inlet structure 14.Aperture 45A extends from the nozzle discharge opening 63 to a point 65'upstream on the exhaust section. Again, the width of the apertureopening 45A should be greatest at terminal opening 63 while the slot 45Atapers along lines 64 and 64a to point 65 where they converge andterminate. FIG. 6 shows dashline 67 which indicates the size of theaperture at section 6-6. The width of the opening 45A should be greaterthan the width w of the exhaust or nozzle section 14A at the pointof-its greatest width. FIGS. 7 and 8 show the cross sections of thenozzle at sections 7-7 and 8-8.

Again, it is preferred that the inner surface 66 of theexhaust nozzle14A opposite the aperture 45A be curved. This is again to afford optimumoperational results and as previously noted, the slot 45A will servesome function of conditioning energy passing through opening 63 withoutthis configuration of the wall opposite it.

FIG. 9 shows how the same principles can be applied to a multiplicity ofjet nozzles 48 in the event that a very short noz zle assembly isrequired in relationship to the total width of the jet. exhaust opening.The width and length (and rate of flare) of the tapered apertures usedmust then be related to the width and length of the individual exhausttubes, as described and shown in order to realize the full effectivenessof this approach. The conical tip on this assembly will assist inreducing turbulences at the end of the array. Various groupings of theseindividual exhaust tubes may be made to attain the most favorabledirectivity patterns for the particular applications involved. Inapplication, such assemblies may be attached to the jet engine 50 withthe aid of an adapter section 51.

In reviewing this invention in relationship to propulsion, and in viewof the experimental data now accumulated and shown herein, it is nowobvious that this invention may be adapted and used in a great manyrelated applications such as rocket engines, automobile mufflers andtheir kin, hydrojet engines, and a great number of nozzle applicationswhere the cited characteristics are of value.

The tapered aperture termination of the exhaust tube, FIG. 2-45 showncan perform these functions and therefore when incorporated into suchengines should perform these very desirable results. The exact design ofsuch tapered aperture nozzles would, of course, depend on many variablesincluding the final directivity and concentration of gaseous flowconsidered optimum for a particular application. In this respect, thediscussions relative to the directivity of sound waves emanating fromtapered apertures in the aforementioned copending applications Ser. No.486,392 and Improvement in Acoustic Transducers have been found to alsoapply to this case insofar as propagation of noise is concerned eventhough the velocities (of flow) involved may well exceed the velocitiesof sound. In any event, the effect of such tapered aperture nozzles willbe to fan out the gaseous flow in one plane and to concentrate it in theother plane. This effect can be used to advantage in noise control sinceif little of the energy is directed downwardly and the major portion ofit fanned out, the intensities in the vertical plane will be minimizedand those in the horizontal plane less concentrated. This is ofparticular value in flying over heavily populated areas, since theloudest noise will occur at the height at which the plane is traveling,and relatively little will be propagated downwardly. Control of thisthickness and fanned flow are accomplished by varying the length of thistapered aperture A and the contour of the walls 66 opposing the taperedstructure. In order to avoid resonance to the maximum degree. the lengthof this tapered aperture should be at least a major portion of theeffective length of the combustion chamber and nozzle, and the finalwidth of this tapered aperture should be a major portion of theeffective internal width at the end of the nozzle. These latterrequirements coincide with those cited in my original patent on acoustictransducers, previously mentioned. The rate of flare at this taper mayvary with different requirements. Early experimentation established thatwhen the width across the taper varies as the square of the length, veryeffective results are achieved.

Under the conditions of air intake, the reciprocal relationships of thisprojector-receptor are again realized. Because of the larger intakearea, more air can be scooped up at a given speed and altitude, andsince this tapered aperture 43 is nonresonant and will gradually packthe air until maximum pressures are realized, there will also be aminimum turbulence and noise attendant to this operation. Also, sincethis scooping process has a gradual packing effect, more air can bemoved through the engine and thus again improve its efficiency andcapabilities for operation at very high speeds. Also, since the airintake will be strongest at the level of the engine due to the fannedinput effect, there will be less hazard to personnel working on decks inthe vicinity of such air intakes.

FIG. 10 shows the tapered aperture 102 of the invention embodied in afire hose nozzle 100.

FIG. 11A and B show the tapered aperture 102 of the subject inventionembodied in fluid injectors.

FIG. 12 shows the tapered apertures 115 and 114 of the subject inventionembodied in the inlet section 106 and exhaust section 104 of a hydrojetassembly 111 respectively. The bottom 111A of the assembly 111 can beshaped to provide a planar surface, and the aspiration at inlet taperedaperture 115 and exhaust tapered aperture 114 will help provide it.

FIG. 13 shows the tapered aperture 119 of the subject invention embodiedin an automobile and tail pipe 118 with muffler 117 and exhaust pipe116.

A sophistication of the basic tapered aperture design is the inwardlyrolled edge presented in FIGS. 14 and 15 in nozzle or inlet 120. Thismodification will much eliminate edge tone noise. This is most importantin the tapered aperture 122, but can also be helpfully employed at theend of the opening at 123.

FIG. 16 shows a rocket 124 including a tapered aperture 125, while FIG.19 illustrates a rocket 141 including a nozzle portion 142 having atapered aperture 143.

As noted previously, in addition to the reduction in noise created byfluid propulsion engines, the subject invention improves the efficiencyof the engine. It has been found that the tapered aperture whenincorporated in the exhaust nozzle of a jet engine will effectivelyimprove the thermal exchange by the mixing of a greater amount ofambient air with the exhaust flow well in advance of the exhaustopening.

Additional thrust efficiency is realized by the aspiration effect theexhaust gases have on the ambient air and the boundary layer airadhering to the nozzle exterior. The aspiration effect reduces the dragon the nozzle surface and in addition creates a negative pressure on thesurface about the tapered aperture. Consequently, when the taperedaperture is on the upper side of the nozzle, a negative pressure isformed on the upper surfaces, thereby directly improving lift.

A final direct benefit of the strong aspiration effected by exhaustgases passing over the tapered aperture is the addition of a componentof massto the propellingforce. This effect is similar to theintroduction of bypass air into the exhaust to increase total propellingmass.

Similarly, additional thrust efficiency is realized by providing thetapered aperture in the air inlet. First of all, the increasedefficiency of the inlet affords means for greater air intake. Also, aircan be accepted from many angles while avoiding acceptance of air fromother angles. This feature is particularly desirable to avoid ingestionof foreign matter or turbulent streams into the turbine section of anengine.

By proper orientation of the tapered aperture in the inlet thecompressor noise can be directed away from approach areas.

In addition, the aperture directly reduces the weight of the inlet andexhaust sections and provides a smaller surface to which friction forcesmay adhere.

Another benefit of the tapered aperture is the fact that thrust is notlimited by supersonic choke since the throat section in the inletadvances or retreats automatically as a function of the speed of theaircraft and conditions attendant thereto. In determining theeffectiveness of thesedevices as air inputs and exhausts an analogue inthe jet engine is found to be helpful. An ordinary tank-type vacuumcleaner was found to be suitable as such an analogur. Test factors usingthe tapered aperture design described in this specification wereemployed in comparison with simple tubular structures representing thetypical exhaust and intake systems of jet engines. in conducting thesetests it 'was found that as an exhaust nozzle, the tapered aperturedescribed herein resulted in approximately a l2 percent increase inthrust relative to a straight tube of the same long length (3 feetlong). Exhaust nozzles of the tapered design increased the thrust .byalmost equal amounts (1 foot long). An exhaust nozzle .of the tapereddesign is shown in FIG. 17, with the nozzle 116 including an aperture128 and a tapered extension 127. In conducting tests on the noisecharacteristics of these exhaust nozzles it was found that the taperedaperture nozzle was able to create an acoustic shielding effect in onedirection and selective dispersion of the high frequency content of thesound in the other direction. It was also found that, the basiccharacter of the sound generated in this exhaust wasconsiderablydifferent from that of a straight tube. its nature might be described ashaving a random or white noise spectrum which is similar to thehiss ofescaping steam, whereas the straight tube was inclined to generate noiseof a specific frequency content relative to its length, and this is theone-note roar to be characteristic of jet engines. The dispersioncharacteristics of a straight tube were relatively omnidirectional aboutits axis with maximum intensities occuring at approximately 45 off axis.This phenomenon is shown in FIG. 18 wherein the noise dispersion 140 ofa straight tube is directed 45 tothe longitudinal axis. In a flight on aplane this would mean that the maximum intensities of thesound would bedirectly propagated down into residential areas whereas the patternofthe tapered aperture is asymmetrical relative to the axis with apreponderance of the sound occuring in a radial dispersion patterndisplaced from the axis toward the side of the tapered aperture and ifthe tapered aperture is facing upwardly, the sound will be dispersedupwardly. By comparison it canbe seen that the greatest intensities ofthe tapered aperture nozzle can be directed upward away from the ground,although the tapered aperture can be differently oriented, if desired.This acoustic shielding effect of the tapered aperture nozzle is furtheraccentuated by an increase in the length of the tapered opening,therefore, it can be anticipated that larger engines using this devicecan be provided with greater acoustic shielding. The acoustic shieldinghas been found to be a function of the number of wave lengths includedin the length of, the tapered opening, therefore, greater acousticshielding is afforded of the high frequencies.

Since these high frequenEies aie most annoying to those who hear thisnoise, and since they can be directed upward, and since they are subjectto the greatest attenuation in the air, and since the spectrum of theresulted noise of the exhaust has been changed, the overall effect onthose who listen to or hear the properly oriented vacuum cleaner analog,(and it is believed to be the expected effect on those who will hear theeffect of the jet engine equipped with this nozzle), will beconsiderably more tolerable and less noisy.

One of the important functions of an exhaust nozzle is the ability tohandle exhaust gases at a considerable variety in velocities. inexamining this feature relative to that of a standard tube of the samediameter, it was found, for example, that a two inch tube would choke inthe vicinity of 20 to 30 pounds stagnation pressure. In conducting thissame test with the tapered aperture nozzle, pressures as high as 100pounds stagnation pressure were impressed on this nozzle without anyevidence of choke effects. This signifies the possibility that this typeof exhaust may be instrumental in creating miniature designs for a jetengine or in the realization of a much greater latitude in thrust ofexisting jet engines. It is also thought that this nozzle will give moreuniform high efficiency over a wide range of power and thrustapplications so that oxygen enriched after burner assemblies can beprovided for withoutsacrificing efficiency of operation at normal levelsof power application, all enabling jet aircrafts to operate more freelyin emergencies and accelerated climbs from an airfield.

Another feature to be taken into consideration in the operation of anyexhaust'nozzle is the effective line of thrust of the exhaustgases-Using the vacuum cleaner analog it was found by suspending a lightstring in the exhaust fluid that this string stretched out atapproximately an angle of l to 2 above the,

axis of the tapered aperture nozzle, and further studies using thestring. as a guide for differentiating between laminar flow andturbulent flow it was seen that laminar flow occurred substantiallyaxially with that of the configuration itself. Some turbulence wasobserved above this flow, whereas below the tapered aperture thereappeared to be a complete absence of turbulence. This indicates that thenoise created by the turbulence above the tapered aperture may also beshielded by the laminar flow of the nozzle itself still further reducingthe noise propagated downward. This feature is illustrated in FIG. 21

wherein a nozzle l49 includes a tapered aperture 151, with dotted linedepicting the boundary between the laminar flow and the turbulent flow,while line 148 depicts the effective line of thrust of the exhaustgases.

Still another characteristic of the tapered aperture nozzle 146 (SeeFIG. 20) as found in the vacuum cleaner experiments was its unusualaspiration qualities. Air 144 would be drawn into the aperture 147 as aresult of the higher velocity flow within the aperture and instead ofair exhausting from the narrow portion of the exhaust it was actuallyfound that air would be drawn into it, and pressure profile tests wereconducted to substantiate this fact and it was found that thisaspiration occurred quite uniformly along'the entire length of thetapered aperture just above the laminar flow lines. This aspiration hasthree principle advantages in that, (1) it increases the thermalexchange between the exhaust gases and the ambient air, (2) in that itcreates additional lift and (3) it increases thrust in that greater massis set into motion by virtue of the exhaust velocities within theexhaust nozzle.

The thermal exchange characteristics of the tapered aperture nozzle areinteresting in that there is half as great a distance at which a returnto ambient occurs than with a straight tubular nozzle. In practice, thismeans that jet engines can be housed in more confined quarters andoperated with greater safety toward associated personnel. Since the rateof thermal exchange is consequently much greater, the jet engine willtherefore operate at a greater overall thermal efficiency and economy offuel.

The lift characteristics of the tapered aperture nozzle may beparticularly advantageous in fast liftoff from an airfield and may alsoreduce wing size required at other velocities.

Reduced wing size in turn would cut down on their drag and thus createthe possibilities for still greater speeds.

The increased thrust through aspiration can be explained as beingcreated by added mass of air set into motion by the tapered aperture. Inanother sense, the tapered aperture nozzle creates a greater couplingbetween the engine and the ambient air.

The velocity pressure profiles were taken of both the straight tubenozzle and the tapered aperture nozzles. As a result of these tests itwas shown that the terminal velocities of the air exhausted from thevacuum cleaner analog with the tapered aperture exhaust nozzle wereconsiderably less than those exhausted from the same analog but from thestraight tube nozzle with the same vacuum cleaner supplying the pressurein both cases. At the same time the tapered aperture demonstrated anincrease in thrust of approximately 12 percent over that of the straighttube nozzle.

An examination of the velocity profiles in both instances showed thatthe greatest velocity accelerations in the tapered aperture nozzle wererealized within its confines whereby the nozzle structure shielded anddirected the noise. The straight tube nozzle on the other hand producedits greatest velocity change at some point external to the tube itself,whereby noise characteristics generated by these higher velocity changesoccur too late to be shielded by the nozzle construction.

A study of the temperatures within the tapered aperture nozzle showedthat the areas closest to the aperture opening were considerably coolerthan those at the opposite wall. This combined with the velocity profilemeasurements indicated that a vena contracta existed within the nozzleitself to form an automatic convergent-divergent nozzle with the shapeof such convergence and divergence being variable with the velocitiesinvolved. With the presence of this vena contracta within the taperedaperture nozzle it is possible to operate nozzles of a relatively fixeddiameter at supersonic velocities. In addition, the shape of the taperedaperture nozzle is such that it will have less drag than that of abell-shaped convergent-divergent nozzle as is commonly used withsupersonic aircraft. Again, this feature will increase the resultant netthrust of existing exhaust configurations.

Air inlets using the tapered aperture design also have some very strongadvantages. When a tapered aperture air inlet was used in combinationwith a tapered aperture exhaust in the analog vacuum cleaner system, theincreased thrust compared to a corresponding combination in straighttubing amounted to approximately 18 percent. One of the problems withair inlets is that of scooping air that is incident to the inlet atvarying angles, the angles normally varying as the planes angle ofattack. A straight tube inlet would be receptive to relatively narrowangles of attack by the ambient air, whereas the tapered aperture inlethas demonstrated that it can accept air from a great variety of anglesand can also reject air from other angles. The action in a sense issimilar to that of its use as an exhaust nozzle with the exception thatthe flow characteristics are such that air at these greater angles ofattack can be accepted. Again the tapered aperture nozzle can also actas a shielding from undesired turbulences by facing the solid sectiontoward these undesirable turbulences. Because the effective area of thetapered aperture inlet is greater than that of a simple tube of the samediameter and because it can accept air at greater angles, it willtherefore accept a greater quantity of air than that of the straighttube design. In addition, because of air inlet is again of a nonresonantstructure, it is capable of operation at a great range in velocitieswithout the necessity of adjustment of the configuration of the airinlet as with some supersonic planes now in use. The resultant action asan air inlet is to gradually increase the pressure as the air is takeninto the inlet, and with this increased pressure, velocities aregradually reduced until a stagnation pressure can be approximated. Sincethe thrust of a jet engine is also strongly a function of the efficiencyof the air inlet, the use of a tapered aperture inlet is highlydesirable both for increasing thrust and for use of a plane at a rangeof velocities from the supersonic to the hypersonic. It is understoodthat most air inlets now in use do not have this range of operationwithout the necessity for adjustment in flight.

The air inlet also can be used to reduce noise by virtue of the factthat again it is nonresonant and would therefore produce very littlenoise due to its structural configuration and also since it is capableof radiating the sounds originating from a compressor in a directionupward of the axis of the nozzle and thus away from the ground when theinlets tapered aperture is oriented upwardly. This upward angleincreases as the plane slows, and its angle of attack increases, as isusually the case in the low altitude maneuvering and landing and takingoff. The uniform acceptance of air at all velocities also contributes tothe safety of operation in a plane as there are no discontinuous effectswhich can serve to choke the air inlet.

in the foregoing discussion and drawings, an attempt has been made todisclose the inlet and nozzle construction which has been found to work,to produce increased thrust with lessened noise of a more desirablefrequency spectrum that may be directed away from sensitive areas. Manyexperiments have been conducted which establish that as a practicalmatter, dramatic results are achieved. In addition, there has been anattempt to set forth the present best understanding of how and why thisinlet and nozzle operate to achieve these advantages. It should beunderstood that the phenomenon are difficult of understanding and notcompletely understood. They are included in an effort to give thoseskilled in the art the full benefit of the present thinking, and withthe understanding that it is to be expected that with additionalexperimentation, data, and analysis, some of this understanding willquite possibly prove to be inadequate and in need of modification.

lclaim:

1. Ducting associated with a fluid reaction propulsion engine fortransmitting a flow of fluid generally along the longitudinal axisthereof and with an opening at one end thereof, said ducting having anaperture disposed therein, which aperture extends from said openingsubstantially parallel to the longitudinal axis of said ducting for amajor portion of the effective length of said ducting, and said aperturehaving a width adjacent said opening of at least a major portion of thetransverse width of the ducting and which converges to gradually closeover the ducting in a direction extending from said opening to aterminal location where the transverse width of the aperture is a minorportion of the transverse width of the ducting in the vicinity of saidterminal location, whereby said aperture defines with said opening aflow passage environment for said flow of fluid.

2. Ducting as recited in claim 1 wherein said aperture has a widthadjacent said opening which is substantially as large as the width ofthe ducting.

3. Ducting as recited in claim 1 wherein the width across the aperturevaries as the square of the length of said aperture.

4. Ducting as recited in claim 1 wherein the width across the aperturevaries at a gradually increasing rate from a point toward the end of theapparatus opposite the opening in said ducting to a width greater thanone-half the width of said ducting whereby the development of standingwaves in said ducting is impeded and the sound noise generated inducting is dissipated evenly and the impedance of the ducting is thuscoupled and matched to that of the atmosphere.

5. An exhaust nozzle for transmitting a flow of fluid with respect to afluid reaction propulsion engine comprising a tubular body memberextending for a predetermined effective length along the longitudinalaxis thereof from said engine, said tubular body member having adischarge opening at one end portion thereof, said tubular body memberhaving an aperture disposed therein and extending from said dischargeopening substantially parallel to the longitudinal axis of said bodymember for a distance at least one-half the effective length of thetubular body member toward said engine, said aperture being tapered andhaving a width which converges with respect to the corresponding widthof the tubular body member in a direction extending from said dischargeopening to a terminal location where said width is a minor portion ofthe width of the tubular body member in the vicinity of said terminallocation, whereby said aperture defines with said discharge opening apassage for said flow of fluid.

6 An exhaust nozzle as recited in claim wherein said aperture in saidtubular body has a width at said discharge opening which is greater thanone-half the width of the tubular member.

7. An exhaust nozzle as recited inclaim 5 wherein the width across thetapered aperture varies as the square of the length of said aperture.

8. An air inlet associated with 'a fluid reaction propulsion engine fortransmitting a flow of fluid with respect to said fluid reactionpropulsion engine comprising a tubular body member extending for apredetermined effective length along the longitudinal axis thereof tosaid engine, said body member having an inlet opening at one endportion, said body member having an aperture disposed therein, whichaperture extends from said inlet opening substantially parallel to thelongitudinal axis of said body member for a distance at least one-halfthe effective length of the body member toward said engine, saidaperture being tapered and-having a width which converges with respectto the corresponding width of the tubular body member in a directionextending from said inlet opening to a terminal location where saidwidth is a minor portion of the width of the tubular body member in thevicinity of said terminal location, whereby said aperture coacts withsaid inlet opening to provide a flow passage for said flow of fluid.

9. An air inlet as recited in claim 8 wherein the width of said apertureat said inlet opening is greater than one-half the width of the bodymember.

10.An air inlet as recited in claim 8 wherein the width across thetapered aperture varies as the square of the length of said aperture.

-11. A nozzle device forgas jet propulsion apparatuscomprising structureforming a tubular body member, said body member having an inlet openingat the upstream end portion thereof for receiving a flow of gas from thepropulsion apparatus and an outlet opening at the downstream end portionof said body member positioned opposite said upstream end portion fordischarging the flow of gas in the form of a jet, the opposite edgeportions of said outlet opening forming, from a point of closure of thetransverse cross section of said body member, a vertex in the wall ofsaid body member at a location upstream of said downstream end portionthereof and progressively diverging from one another in the downstreamdirection until they are separated by the corresponding maximum width ofthe body member and then further opening the aperture by converginguntil said edge portions of said outlet opening join one another at saiddownstream end portion of said body member at a point on the oppositeside of the body member from the point of closure, whereby the portionof said outlet opening having ,a progressively increased area inresponse to the progressively diverging then converging edge portionsthereof is adapted to condition the gas flow in a manner to attenuatethe noise level therefrom.

12. A nozzle device as recited in claim 11 in which said tion and inwhich said opposite edge portions of said outlet opening extenddownstream from said vertex at one side of said duct to the joining ofsaid edge portions at said downstream end portion at the opposite sideof said body member, said edge portions progressively diverging from oneanother in a downstream direction to a point along each of said edgeportions intersecting a common diameter of said body member andprogressively converging toward one another ina downstream directionuntil they join.

13. A sound suppression exhaust nozzle for a fluid reaction propulsionengine comprising an elongated tubular body member of predeterminedeffective length and having an upstream end for connection to saidengine and a downstream end forming a discharge opening, said tubularbody member having a single unobstructed tapered aperture dis osedtherein and extending from said discharge opening su stantially parallelto the longitudinal axis of said body member for a distance at leastone-half of the effective length of the tubular body member, saidaperture having a width which gradually converges with respect to saidtubular body member in a direction extending from said discharge openingand which is greater than one-half the width of the body member in thevicinity of the discharge opening to a terminal location which is aminor portion of the width of tubular member in the vicinity of saidterminal location, whereby said aperture dfl1'lCS with said dischargeopening a flow passage for the engine exhaust gases thereby preventingthe development of resonances in the body member, enabling theaspiration of free stream air into the engine exhaust gases, andcontrolling the directivity of the resultant sound.

14. A sound suppression exhaust nozzle for a fluid reaction propulsionengine comprising:

an elongated substantially tubular duct having an engine end adapted forconnection to said engine and a free end in communication with theambient fluid in which said engine is designed to operate;

said duct having inner and outer surfaces;

a single elongated gradually tapered aperture providing a graduallyenlarging opening between the inside and outside of said duct;

said aperture extending from said free end substantially parallel to thelongitudinal axis of said duct for at least one-half the effectivelength of said duct;

said aperture having an width which, adjacent the free end, issubstantially as large as the duct in the vicinity of the free end;

said aperture having a width which approaches a minimum width at itsopposite to said free end; and

said aperture having a width which progressively diverges in a directionextending from said terminal location to said free end, so as togradually open the passageway inside the duct to the ambient fluidoutside the duct, the width of the aperture being a gradually increasingproportion of the corresponding width of the duct as the free end of theduct and aperture are approached, whereby the inner surface of the ductis in uninterrupted gradually increasing communication with the mediumsurrounding the outer surface thereby preventing the development ofresonances in the duct, and controlling the directivity of the resultantsound.

P0405) UNITED STATES PATENT OFFICE 5 9 CERTIFICATE OF CORRECTION PatentNo. 3,5 6,876 Dated December 1, 1970 Invent fl Karlson. John E.

It.is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

It Column t, line 55, "accomplished" should be --accompanied-- At Column9, line 5 4, following footnotes omitted:

*From the tapered aperture side **Opposite the tapered aperture sideSigned and sealed this 13th day of April 1971.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting OfficerCommissioner of Patents

